Lettuce

Lettuce,  生菜, 萵苣  ( Lactuca sativa ) is a temperate annual or biennial plant of the daisy family Asteraceae. 

Both English name and Latin name of the genus are derived from ‘lac’, the Latin word for ‘milk’, referring to the plant’s milky juice.

The lettuce planted for food is harvested when it’s young and before bolting.  It is typically eaten raw in the West.  In China, it is eaten cooked.

There are 6 commonly recognized cultivar groups :  

Butterhead ( Lactuca sativa v. capitata )

Forms loose heads. Leaves have buttery texture.  Popular varieties include Boston, Bibb, Buttercrunch, Tom Thumb. etc

Chinese Lettuce / Celtuce ( Lactuca stiva v. asparagina )

Long, sword-shaped, non-head-forming leaves.  Bitter and robust flavour.  Popular varieties include 油麥菜, 生菜.

Crisphead / Iceberg

Forms tight, dense heads resemble cabbage.  Crunchy texture.  Popular varieties in America include Tom Thumb, Mini Green, red Rosa, red Rosy, New York, Great Lakes. etc

Looseleaf ( Lactuca sativa v. crispa )

Tender, delicate, mildly flavoured leaves.  Popular varieties include Oak Leaf, Lollo Rosso, Black Seeded Simpson, Ibis, Red Sails, etc

Romaine / Cos ( Lactuca sativa v. romana )

Long, broad, upright leaves.  Popular varieties include Parris Island, Valmaine, etc

Summer Crisp / Batavian.

Forms moderately dense heads with a crunchy texture.